This application relates to the art of refractory compositions and refractory bricks. The invention is particularly applicable to refractory compositions and bricks intended for use in rotary cement kilns. However, it will be appreciated that the invention has broader aspects, and that the improved composition and brick of the present application can be used in other environments and for other purposes.
It is known that the properties of refractory brick for use in rotary cement kilns can be enhanced by the addition of chromium oxide to the brick composition. However, environmental concerns about toxic chromium compounds has restricted the use of such compounds in refractory bricks. This is because toxic chromium compounds may be released to the environment by kiln exhaust emissions and by the disposal of spent refractory linings.
Alternatives to MgO-chrome bricks have included MgO bricks, MgO-CaO and dolomite bricks, and MgO-spinel bricks. MgO bricks are not usually used in cement kilns because of undesirable high thermal conductivity and high thermal expansion. MgO-CaO and dolomite bricks have been successfully used in the center burning zone, but have not generally proven successful in the upper and lower transition zones on either side of the center burning zone. MgO-spinel bricks have most frequently been used in place of MgO-chrome bricks in the transition zones. The performance of MgO-spinel bricks has generally been satisfactory in the upper transition zone, but not in the lower transition zone.
It would be desirable to have a refractory brick to replace MgO-chrome bricks.